ES371280A1 - Die and method for drawing metal tubes - Google Patents

Abstract

A die 17, Fig. 3, for drawing a tube on to a tapered mandrel is composed of a non-metallic plastic material capable of stretching radially and being contracted back to its original annular form. In one embodiment the smaller end of the tapered mandrel with a tube thereon is threaded through the die 17, e.g. of nylon, and fluid pressure from a line 41 is supplied through a die holder 37 and into a groove 33 in the die. The die land 29 is thereby contracted against the tube which is collapsed on to the mandrel. The tube is drawn through the die by an hydraulic cylinder and as the die orifice diameter is increased by the increasing mandrel diameter, the original land area 29 is buckled outwardly from the tube, Fig. 4, and the effective land progresses towards the entry end of the die. The backing pressure is maintained constant during drawing by draining fluid from the chamber 33 through a pressure relief valve (44), (Fig. 1, not shown). In another embodiment, the tube is drawn from a large to a small diameter by first drawing a tapered extension (49) (Fig. 9, not shown) of the mandrel through the die which is thereby expanded. After collapsing the tube onto the mandrel by supplying fluid pressure to the chamber 33, the drawing of the tube is initiated, the die being contracted progressively around the tube. Additional fluid is supplied to the chamber 33 through an accumulator (53) to compensate for the pressure loss due to the contracting die. The die may be strengthened by fingers (54) (Fig. 12, not shown) spring-urged into the groove 33.